All 3d printed Dart LED ring

You will need to print the ring modell in total of eight times, or print the given gcode four times. The holders have to be printed four times or you just print out the given gcode, which includes the four holders. If you like more holders just print them.

You can use the described magnets belowe or you use the insert for the foot to clamp your foot in between the  board and the surround. 
Except that you will need four neodym magnets (25mmx8mmx3mm) to fit into the holders and to connect the holders to the dartboard and an LED stripe.

I also would made a bit of glue at the connection points of the different parts to ensure a tight grip of the parts.